This invention relates generally to automatically controlled article treatment systems utilizing an indexing type conveyor to transport articles automatically into and out of stationary positions where the articles are to be treated, and more particularly relates to an improvement in the control system used to activate the treating device. Such a treating device could be a dispenser or spray coating gun. While this invention has application to many diverse types of treating systems, in one embodiment the system is used for spray coating beverage cans. By way of example the system will be described in terms of its use for spray coating cans. The system has special application in article treatment apparatus which conveys multiple articles simultaneously and serially to multiple independent treating stations for simultaneous treatment, and where there exists the possibility that one or more of these multiple treating stations might not contain an article to be treated in any given treating cycle. The details of this and other advantages of the invention will be described shortly.
As stated above, the automatically controlled article treatment system includes an automatic indexing type conveying system. By an "indexing type" conveying system is meant a system which moves articles in equally spaced pockets, niches or the like, wherein the conveyor advances by some multiple of the spaces between pockets, then ceases to advance for a predetermined dwell time, then advances again by the same amount, and repeats the sequence continuously. The purpose of the sequence could be, for example to bring one or more of the pockets to a specific location so that the articles in these pockets can be treated by stationary treating devices such as automatic spray coating guns. The conveyor may be such that it simultaneously transports multiple articles to a corresponding number of treating stations. If two treating devices are used to simultaneously treat the articles in two adjacent pockets then the conveyor would be adjusted to advance by twice the distance between pockets on each move. The dwell time is predetermined by the time required for the treatment to be completed. Although it has been stated above that the conveyor ceases to move during the predetermined dwell time, it should be noted here that this statement is not meant to imply that the article is necessarily totally stationary. For example, in a system for spray coating cans the can may be spinning in a stopped pocket while the coating process is being carried out.
Generally, control systems of this type are used in a manufacturing environment. Such an environment is generally electrically noisy. The term "electrically noisy" means that such environments contain or are subjected to stray unpredictable electromagnetic fields, etc., which generate undesirable electrical currents and voltages in control circuits.
The general approach to actuating treating devices in an automatic system as described above has previously been done as described in the Straw U.S. Pat. No. 3,521,598. Prior art devices, such as that, control the actuation of treating devices by means of a sensor or mechanical linkage responsive to a cam on the drive mechanism of the indexing conveyor. The cam or mechanical linkage in a predetermined position would indicate that the conveyor was in the proper position for articles to be treated. The articles were treated whenever the cam or mechanical linkage indicated that the conveyor was in a proper position. If there was a possibility that an article could be missing from a given treating position, a second sensor responsive to the presence or absence of the article was required in order to inhibit actuation of the treating device.